Method of operating LC sensors, corresponding system and apparatus

ABSTRACT

In one embodiment, an inductive/LC sensor device includes: an energy storage device for accumulating excitation energy, an LC sensor configured to oscillate using energy accumulated in the energy storage device and transferred to the LC sensor, an energy detector for detecting the energy accumulated in the energy storage device reaching a charge threshold, and at least one switch coupled with the energy detector for terminating accumulating excitation energy in the energy storage device when the charge threshold is detected having been reached by the energy detector.

BACKGROUND

Technical Field

The description relates to inductive (LC) sensors.

One or more embodiments may apply to LC sensors for use, e.g., in fluidmetering applications, such as water and gas meters.

Description of the Related Art

Inductive sensing is based on an inductor-capacitor resonant circuit(which explains the current designation of “LC sensing”) which is pumpedby an oscillator with the inductor acting as a sensing coil. As aconductive (e.g., metal) object comes in the vicinity of the coil,currents are generated in the object depending on various parameterssuch as, e.g., the material and dimensions of the object and/or thedistance to the sensing coil. The currents thus generated form amagnetic field which reduces the oscillation amplitude of the resonantcircuit (tank) thus changing the parallel resonance impedance of thecircuit. Detecting/measuring such change may be exploited for varioussensing purposes.

Inductive/LC sensing may be used in various industrial fields for, e.g.,various types of contactless sensing of moving parts for variouspurposes such as detecting/measuring distance, speed or flow.

For instance, inductive/LC sensing is being increasingly applied, e.g.,in water and gas meter applications with the possibility of offeringpower/efficient solution adapted to be directly embedded, e.g., inmicrocontroller units—MCUs.

In such a possible context of use, factors such as, e.g., reducing thenumber of (analog) components coupled with the sensor, facilitatingdigital processing of the sensing signals and simplifying control logicwhile providing reduced consumption may play a significant role.

Reducing the time involved in performing a certain measurement and/orthe capability of handling multiple sensors represent a further factorsof interest.

Time-based LC sensor excitation using, e.g., a high-speed (e.g., 4 MHz)clock source to control transfer of energy during excitation has beenused with potential drawbacks represented, e.g., by power consumptionand total measurement times in the range of, e.g., 50 microseconds.

BRIEF SUMMARY

One or more embodiments are directed to a method that includesaccumulating excitation energy for an inductive-capacitive (LC) sensor,oscillating the LC sensor using the excitation energy accumulated,detecting the excitation energy accumulated reaching a charge threshold,and terminating accumulating the excitation energy for the LC sensor inresponse to detecting the excitation energy accumulated reaching thecharge threshold.

One or more embodiments also relate to a corresponding system as well asto apparatus (e.g., metering device such as a water or gas meter)including such a system.

The claims are an integral part of the disclosure of one or moreembodiments as provided herein.

One or more embodiments may offer one or more of the followingadvantages:

reduce the power absorption (no high-speed clock needed)

insensitivity to Power Voltage-Temperature—PVT factors, (due to thepossibility of resorting to closed-loop control),

robustness against PVT variations also in the field, that is in currentoperation.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more embodiments will now be described, by way of example only,with reference to the annexed figures, wherein:

FIG. 1 is a generally representative of a possible context of use of oneor more embodiments;

FIG. 2 is a block diagram exemplary of embodiments;

FIG. 3 is a another block diagram exemplary of embodiments;

FIG. 4 is a further block diagram exemplary of embodiments;

FIG. 5 is a another further block diagram exemplary of embodiments; and

FIGS. 6 and 7 are schematic diagrams exemplary of circuit layoutsaccording to one or more embodiments.

DETAILED DESCRIPTION

In the ensuing description, one or more specific details areillustrated, aimed at providing an in-depth understanding of examples ofembodiments. The embodiments may be obtained without one or more of thespecific details, or with other methods, components, materials, etc. Inother cases, known structures, materials, or operations are notillustrated or described in detail so that certain aspects ofembodiments will not be obscured.

Reference to “an embodiment” or “one embodiment” in the framework of thepresent description is intended to indicate that a particularconfiguration, structure, or characteristic described in relation to theembodiment is comprised in at least one embodiment. Hence, phrases suchas “in an embodiment” or “in one embodiment” that may be present in oneor more points of the present description do not necessarily refer toone and the same embodiment. Moreover, particular conformations,structures, or characteristics may be combined in any adequate way inone or more embodiments.

The references used herein are provided merely for convenience and hencedo not define the extent of protection or the scope of the embodiments.

The schematic diagram of FIG. 1 is generally exemplary of possibleapplications of inductive/LC sensing: these designations will behereinafter used as synonyms having regard to the general principle ofoperation of such sensors as summarized in the introduction of thisdescription.

The schematic diagram of FIG. 1 is exemplary of a possible applicationof inductive/LC sensors 10 in a fluid metering device such as aflow-meter (e.g., water or gas meter) in order to detect/measure fluidflow in a conduit C. This may take place, in manner known per se, bydetecting/measuring movement of a rotary sensing plate P which is drivenin rotation by fluid flow in the conduit C.

For instance, the rotary plate P may include complementary portions ofdifferent materials (e.g., conductive and non-conductive). One or moreLC sensors 10 arranged facing the plate P may thus produce signalsindicative of rotation of the plate P (and thus of the flow in theconduit C) for processing in a controller, e.g., a microcontrollerunit—MCU.

The general principles underlying the structure and operation of suchmetering device are otherwise known in the art, which makes itunnecessary to provide a more detailed description herein. Also, it willbe appreciated that the application exemplified in FIG. 1 is just one ofa wide variety of possible applications of inductive/LC sensor 10, oneor more embodiments being otherwise primarily concerned with managingoperation of such an LC sensor.

In one or more embodiments, operation of an LC sensor 10 as exemplifiedherein may generally involve at least one charging phase whereinexcitation energy for the sensor 10 is accumulated. The LC sensor (hereexemplified as the parallel connection of an inductor L_(s) and acapacitor C_(s)) may thus oscillate energized by the energy accumulatedto permit sensing to take place as outlined in the introduction to thisdescription.

In conventional solutions, energy accumulation (charging) may be stoppedat a certain time as defined, e.g., by a high-frequency (e.g., 4 MHzclock source).

By way of contrast, one or more embodiments as exemplified herein mayprovide for detecting (e.g., by a charge sensor/energy meter 12) thefact that the energy accumulated has reached a certain chargeaccumulation threshold, with operation switched towards the sensingphase when the charge threshold is detected to be reached.

In one or more embodiments as exemplified in FIG. 2 the excitationenergy from an electric energy source V (of any known type for thatpurpose) may be accumulated by charging a reference capacitor C_(ref).

One or more embodiments as exemplified in FIG. 2 may include a firstswitch S1 and a second switch S2 (e.g., electronic switches such asMOSFETs) switchable under the control of the energy meter 12 configuredfor sensing the charge on the reference capacitor C_(ref) (e.g., thevoltage across the reference capacitor C_(ref)).

When the switch S1 is closed, that is conductive, the referencecapacitor C_(ref) is set between the source V and ground, and the sensor10 may be set between the source V and the switch S2, with the switch S2set between the sensor 10 and ground.

In one or more embodiments, operation of the circuit layout exemplifiedin FIG. 2 may include:

pre-charge of C_(ref): S2 is open—that is non-conductive—so that thesensor 10 is “floating” with respect to ground, and S1 is closed—that isconductive—until the voltage on C_(ref) reaches a value VC_(ref) _(_)_(INIT) (<=V) with S1 subsequently open—that is non-conductive;

energy transfer: S1 is open and S2 closed, so that the energyaccumulated on C_(ref) is (partially) transferred onto the sensor 10(which is substantially in parallel to C_(ref)). Controlled transfer ofenergy terminates when the voltage across C_(ref) reaches a final targetvalue VC_(ref) _(_) _(FIN), after which the switch S2 is opened. In thatway, the amount of energy transferred is (ideally) equal to 0.5C_(ref)(VC_(ref) _(_) _(INIT)−VC_(ref) _(_) _(FIN))²;

measurement: both S1 and S2 are open. The sensor will start oscillatingaround the voltage value VC_(ref) _(_) _(FIN), with such oscillationadapted to be monitored via the pin towards the switch S2.

The circuit may then be reset and the sequence exemplified in theforegoing repeated for a new measurement.

FIG. 3 is exemplary of the possibility of implementing a similar mode ofoperation in an arrangement where the inner resistance R of the source(generator) V may play the role of the switch S1, by assuming that thetime constant T=R*C_(ref) is much higher than the time needed forperforming the measurement, which is reasonably the case if, e.g., theinternal pull-up of the address data bus or PAD of microcontroller D isused as the voltage generator V.

In one or more embodiments, operation of the circuit layout exemplifiedin FIG. 3 may again include:

pre-charge of C_(ref): S2 is open and the energy meter 12 monitors thatC_(ref) is charged to an energy accumulation threshold voltage, e.g., V;

energy transfer: S2 is closed and the energy accumulated on C_(ref) ispartially transferred onto the sensor 10. Controlled transfer of energyterminates when the voltage across C_(ref) reaches a final target valueVC_(REF) _(_) _(FIN), after which the switch S2 is opened. In that way,the amount of energy transferred is (ideally) equal to 0.5C_(reF)(V·VC_(ref) _(_) _(FIN))². The energy from the generator may beneglected due to the high value of the time constant.

measurement: S2 is open. The sensor will start oscillating around thevoltage value VC_(ref) _(_) _(FIN), with such oscillation adapted to bemonitored via the pin towards the switch S2. The voltage variation onC_(ref) due to re-charging via the generator V may again be neglecteddue to the time constant T=R*C_(ref) being much higher than the timeneeded for performing the measurement.

In one or more embodiments as exemplified in FIG. 4 a referencecapacitor C_(ref) may again be used, by coupling it in series with theLC sensor 10, with the series connection of the sensor 10 and thereference capacitor C_(ref) set between a switch S1 (again an electronicswitch such as a MOSFET: the same designation of FIG. 2 is used forsimplicity) and ground with the reference capacitor C_(ref) between thesensor 10 and ground.

In one or more embodiments as exemplified in FIG. 4, an energy sensingmeter 12 may again be provided capable of sensing the charge on thereference capacitor C_(ref)(e.g., the voltage across the referencecapacitor C_(ref)) and driving the switch S1 which is arranged betweenthe source V and the sensor 10.

In one or more embodiments as exemplified in FIG. 4, the switch S1between the source V and the sensor 10 may be closed (that is,conductive) while energy is being accumulated on the reference capacitorC_(ref) via the sensor 10. When a certain charge threshold is detectedto be reached (as dictated by the characteristics and intended mode ofoperation of the sensor) on the reference capacitor C_(ref) the energymeter 12 may open the switch S1.

In one or more embodiments, operation as described above may involveboth excitation of the sensor 10 and charging the capacitor C_(ref)(that is the sensor 10 is excited by the current flowing throughC_(ref)).

Such a charging/excitation process terminates when the charge, that isthe voltage on C_(ref) reaches a target threshold value.

By way of reference to the exemplary layouts of FIGS. 2 and 3, thearrangement exemplified in FIG. 4 may be regarded as somewhat joiningpre-charge and energy transfer (charge sharing) with excitation of thesensor and generation of the voltage C_(ref) about which oscillationwill occur taking place in a single step.

In one or more embodiments as exemplified in FIG. 4 measurement mayinvolve opening the switch S1, with the sensor 10 starting oscillatingabout the value of the voltage charged onto C_(ref), and the pin towardsS1 (which remains floating since S1 is open) adapted to be used formonitoring the (damped) oscillation, with C_(ref) primarily providing areference for the voltage about which sensor oscillation will takeplace.

The circuit may then be reset and the sequence exemplified in theforegoing repeated for a new measurement.

FIG. 5 is exemplary of the possibility of implementing a similar mode ofoperation by making sensor excitation independent of generation of theoscillation voltage on C_(ref).

In comparison with the exemplary circuit layout of FIG. 4, the exemplarycircuit layout of FIG. 5 involves:

a second switch S2 (again an electronic switch such as a MOSFET: thesame designation of FIGS. 2 and 3 is used for simplicity) set betweenthe sensor 10 and ground, that is in parallel to the capacitor C_(ref);

the energy meter 12 configured for driving the switches S1 and S2 as afunction of the voltage at a point between the switch S1 and the sensor10.

In one or more embodiments, operation of the circuit layout exemplifiedin FIG. 5 may include:

excitation: S1, S2 both closed, with the sensor 10 set between thevoltage V and ground. The energy meter 12 is sensitive to the amount ofenergy transferred; C_(ref) kept uncharged as it is grounded on bothsides;

post excitation and generation of Vref: S1 closed and S2 open. Chargingof the sensor 10 is completed and the capacitor C_(ref) is charged to afinal value VC_(ref) _(_) _(FIN);

measurement: S1 and S2 both open, with the sensor oscillation about thevoltage VC_(ref) _(_) _(FIN), and oscillation adapted to be monitored onthe “floating” pin of the switch S1 opposed to the source V.

Various other implementations are feasible in one or more embodiments.

Just to mention one possibility, in one or more embodiments, the switchS2 may connect directly C_(ref) to the generator V, so that VC_(ref)_(_) _(FIN) may be generated directly instead of via the sensor 10.

The circuit diagrams of FIGS. 6 and 7 provide further details ofpossible embodiments along the lines of FIGS. 2-3 and 4-5, wherein theI/O PADs of, e.g., a microcontroller such as D in FIG. 1 may includeinternal switches S1, S2 (possibly admitting connection to a source Vdd,to ground GND and “open”, e.g., floating) as well as Schmitt triggers141, 142. In the discussion that follows, the microcontroller controlsthe switches S1, S2 based in part on the inputs ZI provided by theSchmitt triggers 141, 142.

In FIGS. 6 and 7 the same reference symbols are used to denote parts ofelements already introduced in connection with FIGS. 2 to 5 withoutrepeating the related description for the sake of brevity.

The circuit diagrams of FIGS. 6 and 7 are exemplary of arrangementsproviding good power efficiency by resorting to “clock-less” operationwhere the excitation time may be controlled by the PAD's via Schmitttriggers and the capacitors Cs and C_(ref), thus dispensing with highfrequency clock sources, with the measurement process adapted to bedriven, e.g., by a low speed real-time clock (RTC) (e.g., low-speedexternal (LSE) clock) that has the basic task of triggering newmeasurements.

The circuit diagrams of FIGS. 6 and 7 are exemplary of twoimplementation schemes:

a clock-less charge sharing scheme, including a pre-charge step where areference capacitor C_(ref) is preloaded by a PAD IO1 with a maximumvoltage (Vdd) and a second step where the accumulated energy istransferred to the sensor 10 to excite and generate the referencevoltage on C_(ref) (FIG. 6); and

a clock-less direct charge scheme, where excitation of the sensor 10 andgeneration of the reference voltage are driven by two PADs, e.g., IO1,IO2, with two charge steps, e.g., pre-charge and post-charge (FIG. 7).

A direct charge mechanism may permit to use a smaller C_(ref) withrespect to a charge-sharing scheme.

In one or more embodiments as exemplified in FIG. 6, the sensor 10 willbe charged by means of a controlled transfer of charge from C_(ref). Inthis case C_(ref) may be selected with a capacity large enough to storean adequate amount of charge for exciting the sensor 10 and to hold aresidual energy in the capacitor (Vmid voltage).

One or more embodiments as exemplified in FIG. 6 may involve twodifferent charge steps: in the former C_(ref) is fully loaded at Vdd andin the latter the accumulated energy is transferred to the sensor 10.

In one or more embodiments, operation of an arrangement as exemplifiedin FIG. 6 may involve the following steps performed to complete ameasurement stage:

reset and pre-charge: both switches S1 and S2 are closed to Vdd, thesensor 10 will be discharged while C_(ref) is precharged to Vdd. Theresidual energy in the capacitor (Vmid voltage) is held and used asstarting point for this step;

charge sharing: the switch S1 is open while the switch S2 is closed toGND. With this configuration C_(ref) provides the energy required toload the sensor 10. This step will be completed when the trigger IO1 (ZIinput) reaches a logic “0” (with the IO1 voltage at VthL). The amount oftransferred energy is 0.5 C_(ref) (Vdd−Vthl)²;

sensor oscillation: both switches S1 and S2 are open and the oscillationmay be monitored via the IO2/ZI pin.

In fact, the voltage Vmid=VthL about which oscillation takes place maybe present on IO1 while VIO2=Vsensor+VIO1=>VIO2=(Vsensor+VthL)/ZI pin.

In the arrangement exemplified in FIG. 7, a single sensor 10 may be setbetween two PADs IO1 and IO2: in one or more embodiments, thatconfiguration may be extended to cover multiple sensors 10 both in 4 PADor 6 PAD configurations).

In one or more embodiments as exemplified in FIG. 7, the PAD IO1 mayhave two main tasks:

providing the current to charge/reset the sensor 10 and C_(ref);

triggering the start of the post-charge phase (IO1 Schmitt trigger 141).

In one or more embodiments as exemplified in FIG. 7, the PAD IO2 mayhave the following main tasks:

discharging the sensor 10 during a reset state;

triggering the end of a post-charge phase looking at its voltage level(Schmitt trigger 142);

tuning and controlling the voltage on C_(ref) during the oscillationtime.

In one or more embodiments, operation of an arrangement as exemplifiedin FIG. 7 may involve the following steps performed to complete ameasurement stage:

reset: switch S1 and switch S2 are closed to GND, both the sensor 10 andthe capacitance C_(ref) are shorted to GND;

pre-charge: the switch S1 is closed to Vdd while the switch S2 is closedto GND. In this initial phase the inductor Ls can be assumed to be anopen circuit for an exemplary sensor 10, with the capacitor Cs setbetween Vdd and GND and C_(ref) connected to GND, so that the sensorcapacitor Cs will be charged; the pre-charge duration will be completedwhen the IO1 trigger (ZI input) reaches, e.g., a “1” logic level, withCs pre-charged to a value VthH so that the energy transferred to thesensor 10 is 0.5 Cs VthH²;

post-charge: the switch S1 is closed to Vdd while the switch S2 is open(high impedance). In this step sensor excitation will be completed andthe reference voltage on C_(ref) generated. The post-charge will becompleted when the IO2 trigger (ZI input) will reach a “1” logic level.At the end of this step C_(ref) will be pre-charged to VthH and thesensor fully charged. For high values of C_(ref) the sensor inductorcurrent may not be negligible, and the PAD IO1 will provide both theenergy for the inductor Ls plus the energy for C_(ref);

Vref range stabilization and oscillation measure: when the IO2 voltagereaches VthH, the switch S1 will be open (end of post-charge step) whilethe switch S2 will be configured to keep the IO2 voltage below VthH: thePAD will drive a logic “0” (PullDown or PushPull depending of registerconfiguration) any time that the IO2/ZI is one. The IO2 configurationensures that the C_(ref) voltage is kept below the VthH voltage value:for instance, for 5 Volt-tolerant PADs there are some parasitic effects(diode) that may increase the Vref voltage during oscillation of thesensors 10 in case this goes below GND. The dumped oscillation will beobserved by the IO1/ZI pin.

In one or more embodiments exemplifies herein, the final part of thesmooth oscillation may cross the trigger threshold (Vth) with a reducedslope, which may expose the device at the noise: some extra pulse can begenerated if a noise with a sufficient amplitude occurs near the Vthcrossing. In one or more embodiments, noise immunity may be pursued byreducing the time over which the smooth oscillation is near the Vththreshold. In one or more embodiments that result may be achieved bymoving the detection phase near the first phase of the oscillation wherethe slope of the waveform is sharpest and/or by moving dynamically theVmid voltage during the measurement time.

The first solution may be applied by reducing the Vmid voltage value.For a clock-less charge-sharing solution as exemplified in FIG. 6 onemay activate the PD on the PAD IO2 to decrease the Vmid voltage duringthe oscillation. A register may be used to select how many pulses arecounted before the PD is enabled, and a register may be similarly usedto enable the dynamic PD feature. For a clock-less solution asexemplified in FIG. 7, during the Vref range stabilization step theIO2/ZI feedback can be “stretched” to reduce the Vmid voltage with aprogrammable delay (e.g., a register).

Without prejudice to the underlying principles, the details andembodiments may vary, even significantly, with respect to what has beendescribed by way of example only, without departing from the extent ofprotection.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

The invention claimed is:
 1. A method comprising: accumulatingexcitation energy for an inductive-capacitive (LC) sensor, oscillatingthe LC sensor using the excitation energy accumulated, detecting theexcitation energy accumulated reaching a charge threshold, andterminating accumulating the excitation energy for the LC sensor inresponse to detecting the excitation energy accumulated reaching thecharge threshold, wherein the accumulating includes: short-circuiting areference capacitor that is coupled in series to the LC sensor, startingaccumulating excitation energy for the sensor by coupling the LC sensorto an energy source with the reference capacitor short-circuited, andremoving the short-circuit across the reference capacitor whilemaintaining the LC sensor coupled to the energy source.
 2. The method ofclaim 1, wherein: the short-circuiting includes closing a switch that isconnected in parallel with the reference capacitor.
 3. The method ofclaim 1, wherein detecting the excitation energy accumulated reachingthe charge threshold includes detecting a voltage across the referencecapacitor reaching a voltage threshold.
 4. The method of claim 1,including a reset step that shorts the LC sensor to a ground terminal.5. An LC sensor device, comprising: an energy storage device configuredto accumulate excitation energy, an LC sensor coupled to the energystorage device and configured to oscillate when energized by theexcitation energy in the energy storage device, an energy detectorconfigured to detect the excitation energy in the energy storage devicereaching a charge threshold, and at least one switch coupled with theenergy detector and configured to terminate accumulating the excitationenergy in the energy storage device in response to energy detectordetecting that the charge threshold has been reached by the excitationenergy in the energy storage device, wherein: the energy storage deviceincludes a reference capacitor coupled in series to the LC sensor; theat least one switch includes a first switch and a second switch, thefirst switch being configured to selectively couple the LC sensor to anenergy source and the second switch being configured to selectivelyshort-circuit the reference capacitor, and the energy detector isconfigured to close the first switch to electrically couple the LCsensor to the energy source and open the second switch to remove theshort-circuit across the reference capacitor while the LC sensor iselectrically coupled to the energy source by the first switch.
 6. The LCsensor device of claim 5, wherein: the second switch is connected inparallel with the reference capacitor.
 7. The LC sensor device of claim5, wherein: the energy detector is configured to detect the energyaccumulated reaching the charge threshold by detecting a voltage acrossthe reference capacitor reaching a voltage threshold.
 8. The LC sensordevice of claim 5, wherein the at least one switch is configured toselectively short circuit the LC sensor to a ground terminal.
 9. The LCsensor device of claim 5, wherein at least one of the energy detectorand the at least one switch is implemented by a controller unit.
 10. Afluid flow sensing device, comprising: a sense structure configured tobe moved by a fluid flow; and an LC sensor device coupled to the sensestructure and configured to sense movement of the sense structure, theLC sensor including: an energy storage device configured to accumulateexcitation energy, an LC sensor coupled to the energy storage device andconfigured to oscillate when energized by the excitation energy in theenergy storage device, an energy detector configured to detect theexcitation energy in the energy storage device reaching a chargethreshold, and at least one switch coupled with the energy detector andconfigured to terminate accumulating the excitation energy in the energystorage device in response to the energy detector detecting that thecharge threshold has been reached by the excitation energy in the energystorage device, wherein: the energy storage device includes a referencecapacitor coupled in series to the LC sensor; the at least one switchincludes a first switch and a second switch, the first switch beingconfigured to selectively couple the LC sensor to an energy source andthe second switch being configured to selectively short-circuit thereference capacitor, and the energy detector is configured close thefirst switch to electrically couple the LC sensor to the energy sourceand open the second switch to remove the short-circuit across thereference capacitor while the LC sensor is electrically coupled to theenergy source by the first switch.
 11. The fluid flow sensing device ofclaim 10, wherein: the second switch is connected in parallel with the areference capacitor.
 12. The fluid flow sensing device of claim 10,wherein: the energy detector is configured to detect the energyaccumulated reaching the charge threshold by detecting a voltage acrossthe reference capacitor reaching a voltage threshold.
 13. The fluid flowsensing device of claim 10, wherein at least one of the energy detectorand the at least one switch is implemented by a controller unit.